Hi everyone. I want to study the transport of a manual wheelbarrow ( I already have the STL file)., and I need to validate its ergonomics (Hand reaction forces, Muscle activity, Joint moments, compression forces).
I would like to ask a few questions to clarify some aspects of the modeling process:
-Should additional contact points be defined between the wheel and the ground or is it acceptable to consider the wheelbarrow as rigidly attached to the hands?
-Since I only have motion capture data from Xsens for the person (not for the wheelbarrow), how can I synchronize or drive the wheelbarrow motion according to the human motion?
-How should the contact between the hands and the handles be defined?
Recap : input the model is the xsens motion, there are no measurement on the wheelbarrow.
Kinematics:
I would model the wheelbarrow as a new segment having contact to hands and ground, letting the motion of the hands drive the wheelbarrow.
The wheelbarrow has 6 DOF, i would add the following kinematic constraints to the wheelbarrow
The following items should be added to the InverseDynamicStudy, i suggest to add the wheelbarrow as a kinematically determined model driven by hands so no need to have it present in the markertracking study.
You can create a new include file to include from you main file, in this include file add all items
Main ={
Studies.InverseDynamicStudy ={
//Add model here...
};
};
Wheelbarrow:
Make a segment representing wheelbarrow add mass and CoM to represent masses.
Add STL for visual
Add a node representing lowest point on the wheel to be used for ground contact
Add nodes in the handles right/left to be used for connection to hands
set r0 and Axes0 of the wheelbarrow segment to provide a resonable loading position wrt to the human.
Kinematics
One linear constraint between wheel and ground vertically
Three linear constraints between right hand and a point on the right handle
Two linear constraints between left hand and a point on left handle. These two directions should represent vertical and longitudinal direction, so not constraining distance between right and left hand.
Kinetics:
Enable reactions to the wheelbarrow vertical constraint and additionally add a reaction force sideways (wheel cannot slide sideways) use a linear measure and AnyReacForce
Hands: add a linear and rotational measure from the node on the handle right/left to the glove segment on the hand Right/Left. Add reaction forces on these measures this will do the contact.
These items should create a wheelbarrow model driven by hands motion and ground contact.
Note that if mass and inertia of wheelbarrow is correct and hand motion is accurate the loads to the hands should be correct. If the motion accelerates the wheelbarrow this force will need to be delivered by the hands (together with the load from gravity).